Adding an edge loop to a pyramid
One quick way is to use Offset Edge Slide tool. Select bottom face and run it (depending on the version) either with Ctrl+Shift+R or via viewport menus:




  Add two edge loops on either side of selected loops.


Offset Edge Slide

Since there aren't any faces on the other side of the selected face before using the command, no extraneous edges will be added and you don't need to dissolve any unnecessary geometry in this case.